When you're looking forward to leaving work early or on time, but are kept late either by a new assignment from your boss or a chatty coworker.

someone who is sexy beyond mean

When you're having a sexual dream and it's interrupted by your alarm clock.

A clock block is a customer or co-worker that asks you a question or distracts you right as you are about to clock off for the day.

Some schools have a time policy for professors which allows students to leave if the instructor does not arrive after a given amount of time. Clock Blocking is when a professor arrives just before this time expires.

when you had the opportunity to get lucky, but are not permitted to due to time constraints

to tell the time before anyone else gets the chance to; similar to the cockblock, but for the current time, not penetration